Make a backup of your "interfaces" file and then try this..
and then reboot......




# The loopback network interface
auto lo
iface lo inet loopback


# The loopback network interface
auto lo
iface lo inet loopback

# The primary wired network interface
auto eth0

# The wireless network interface
auto wlan0
# Maybe should change the above to 
# allow-hotplug wlan0 (from auto wlan0)
# but it should always be plugged in at boot anyway

iface wlan0 inet manual
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf

# the "roam" means with only one network set it will
# try to reconnect if the connection is lost

# Default connection (for all connections)
iface default inet static
address 10.1.1.101
netmask 255.255.255.0
broadcast 10.1.1.255
gateway 10.1.1.1
dns-nameservers 8.8.8.8 4.4.4.4

# dns-nameservers (google) just in case...